1 Peel the tomatoes if they’re fresh. Chop them coarsely and put them in a large saucepan with the onion, butter, salt and basil. Bring to a boil over medium-high heat and simmer gently for 30 to 45 minutes, stirring occasionally.

2 Taste and adjust the seasoning, and remove the onion if you like (or leave it in and just hack it up a little with a sharp knife). Use immediately (sauce can be refrigerated for up to 5 days or frozen for up to six months).